1. Field of the Invention
The present invention relates to a process for producing hydrogen absorbing alloy powder suitable for a negative electrode of an alkaline storage battery, as well as a hydrogen absorbing alloy electrode formed of the hydrogen absorbing alloy powder produced thereby. More specifically, it relates to a process for producing a hydrogen absorbing alloy suitable to the application of a nickel-hydrogen storage battery which excels in properties such as a cycle life and a high rate discharge property.
2. Description of the Related Art
Since a hydrogen absorbing alloy which can charge and discharge hydrogen was discovered, the application thereof has been progressively developed. An alkaline storage battery containing a negative electrode formed of the hydrogen absorbing alloy has been made practicable, and the hydrogen absorbing alloy used for it has been improved one after another.
Although the LaNi.sub.5 alloy investigated initially (Japanese Provisional Patent Publication No. 51-13934/1976) has an advantage that the absorbed amount of hydrogen is large, it also has disadvantages such as expensive La metal and a tendency to become impalpable powder in progress of repetition of charge and discharge of hydrogen. Further, it has such a disadvantage that it is easily corroded by an alkaline solution or an acid solution. Accordingly, when said hydrogen absorbing alloy is applied in an alkaline storage battery, despite an high initial capacity, the capacity becomes no more than a half of the initial capacity after the 50 or more times of charge and discharge cycles. Consequently, the hydrogen absorbing alloy has an disadvantage of being incapable of withstanding a longer period of use.
The disadvantages have been improved by substituting a part of La of the LaNi.sub.5 alloy by Ce, Pr, Nd or other rare earth elements, and/or by substituting a part of Ni of the LaNi.sub.5 alloy by metal such as Co, Al, Mn or the like (Japanese Provisional Patent Publication Nos. 53-48918/1978, 54-64014/1979, 60-250558/1985, 61-91862/1986, and 61-233969/1986).